Primary, To compare with a placebo, the safety of SmithKline Beecham Biologicals' herpes simplex vaccine (gD-Alum-MPL) in healthy adults of any HSV serostatus. Secondary To compare with placebo the reactogenicity of the vaccine. To compare between vaccine and placebo recipients the effect on haematological and biochemical parameters. To compare between vaccine and placebo recipients the effect on pre-existing herpes simplex infection or disease. To evaluate the serious adverse experiences in both groups To evaluate the humoral immune response to the vaccine in HSV seronegative and in HSV seropositive healthy adults.